This invention pertains, generally, to gate-type valves, and in particular to gate-type, line blind valves. Line blind valves are commonly used to blank off pipelines. The traditional method of blanking off pipelines, for service work within a vessel or pipeline, has been to unbolt the pipe at an adjacent flange, and rebolt a blind flange onto the pipe to be sealed. This leaves the downstream pipe or vessel open to atmosphere, and safe for servicing. This is a time-consuming and labor-intensive process.
An alternative approach is to use a line blind valve, namely, a dual, rubber-seated, through-ported valve. Such a valve acts as an extension of the pipeline, in the open position, and in the closed position, it acts as a blind flange, in that any leakage past the valve seal will leak to atmosphere, and not into the downstream pipeline or vessel.
The line blind valves which are currently being used for the servicing of pipelines and such have a major drawback. When the valves are cycled, the media will leak through the seals and, if not contained, will spill onto the ground or pass into the atmosphere.
The problem of media spillage can be solved by placing a pressure-containing shell around the valve seals to contain the leakage. When the valve is in the closed position, the pressure-containing shell must then be opened to function as a line blind, allowing any seal leakage to vent to the atmosphere. A subsequent problem, when using a pressure-containing shell, is to ensure that any solids in the media will not collect inside the shell and plug the body cavities. If the latter should happen, there is the possibility that the media could leak into the downstream pipe or vessel. Any such pressure-containing shell must be designed to contain the pipeline pressure during cycling, but also be configured to be freely open to the atmosphere when serving as a line blind.